For the monitoring of currents and voltages in power technology, due to their high values these must generally be converted into proportional comparison values by means of an intermediary unit, in order to be able to record and analyze them with conventional measuring devices.
In switchgear and switching device technology so-called current converters are known, which in the “plug-in current transformer” format surround a current-carrying conductor in an annular manner and are thus also designated as donut-type current transformers. In accordance with their electromagnetic functional principle, these converters are also designated as a special type of transformer.
Around a core of ferromagnetic material, which surrounds a primary winding comprising the conductor with the current to be determined, runs a secondary winding, to the ends of which is connected a resistance—the so-called load—at which in turn a voltage value proportional to the primary current can be measured.
This value is, for example, processed in electrically monitored circuit-breakers in relation to overload protection for the connected consumers.